This invention concerns a press table insert for a coating press.
For coating form boards, in particular form boards with milled cuts used as front panels in furniture construction, with film on the surface as well as on the edges in a single pass process, press machines are used in which the workpiece is placed on a support whose circumference is slightly retracted with respect to the edge of the workpiece. This makes it possible for the film to nestle not only on the surface into the milled cuts, but also allows it, after applying increased or decreased pressure, to pull down at the edges and finish flush therewith.
Press machines are known for which the supporting body must be specially made for the particular workpiece. This is certainly a satisfactory solution for mass production with workpieces which have constant dimensions. But if the dimensions of the workpiece vary frequently, in particular for special production, very many different supports must be quickly available in this case. This entails enormous work effort and costs.
Press machines are also known which use modular components to produce the required supports.
For example, the document DE 295 00 248 describes a modular components system for plate/board workpieces in which support plugs are inserted into holes according to a given pattern for supporting the workpiece. However, the pattern must be determined and implemented separately for each kind of workpiece, and it can carry only one particular workpiece, like the solid supports. The support must be created new if it is necessary to quickly coat another different workpiece together with the main workpiece in each pressing cycle.
Thereby it makes no difference whether the second workpiece is smaller or larger than the first one, because the same support cannot be used for both workpieces in either case. If the second workpiece is too large, it cannot be supported securely, so that there is a danger that it will break when the applied pressure per unit area is too large. If the second workpiece is too small, the already set plugs prevent proper coating of the edges, because the film cannot be completely pulled down.
The document PCF/DE97/00544 shows a coating press in which the laying table has a table plate with raster breakouts in which movable carriers are inserted. These carriers can be moved out of the table plate to lift the workpiece off the table plate. Furthermore, sensors are provided which determine the size and position of the workpiece. The carriers are actuated via deflecting rockers to generate the support pattern. However, the workpiece is sensed row by row of the carriers before it can be moved up. This is a time-consuming process tending to slow-down production.
This device also requires a complicated expensive control mechanism, and the variability of the workpieces is still restricted by the rather large supporting plates resting on the carriers.
The purpose of this invention is to produce a press for film coating form boards on several sides, avoiding the disadvantages of the known solutions while providing supports for any workpiece quickly and cheaply.
This invention is also intended to provide a solution which can be retrofitted to machines which are workpiece movable through a certain horizontal range of displacement of the press table, and by reducing the height of each individual carrier during the pressing process.
The range of movement assigned to each individual carrier permits an arrangement of the carriers such that workpieces of any shape and size can be coated without first having to define a supporting pattern. It suffices to place the workpieces onto the carriers and then to adjust the positions of individual carriers on the outer edges of the workpieces. This can be done quickly and efficiently because it is not necessary to maintain any exact clearance dimension. The height of each individual carrier is also shortened during the pressing process to assist the latter. This is of advantage in particular because an initially higher carrier brings the workpiece closer to the heating device, so that the radiant heat pre-heats the parts which are to be film-coated, thus ensuring better edge and surface adhesion strength, because the film does not have to be heated as much since the workpiece is already hot. Furthermore, the film coating in the vacuum drawing work step is carried out without any problems while the workpieces are high. When pressure is applied in the next step, the lower height is more advantageous for preventing film problems in the corner regions, in particular wrinkles or tearing of the material. Therefore reduction of the height of the individual carriers during the pressing process is major step towards work process simplification.
In principle, every range of movement around every individual carrier can be made arbitrarily large. This solution can prove to be favorable in particular for making special workpieces as well as for special tasks. Some examples are glass frame pressing, frame pressing in general, film coating of round and polygonal pieces.
For producing standard parts as well as simple rectangular workpieces such as furniture fronts, it is of advantage to make the range of movement equal for all individual carriers. The mutual separations of adjacent ranges of movement can also be made equal. This defines a symmetrical pattern with uniform minimum and maximum mutual separation of the individual carriers. At any rate, it is necessary not to undershoot a minimum separation of adjacent ranges of movement, and this also defines a minimum separation of adjacent individual carriers. Such an arrangement soon leads to problems for coating the workpiece surfaces. This can be combated by providing a minimum separation.
This invention envisages that each individual carrier has the same length and consists of a shaft, a base and a covering layer resting on the base. The shaft and base are preferably made of rigid material, for example plastics such as polyamide or cellamide, or of aluminum, whereas the covering layer consists of elastic material to make possible shortening of the height of the individual carriers during the pressing process. The covering layer also avoids direct contact between the workpiece underside and the rigid material of the base which would not be optimum for taking up the high working pressures and could also damage the workpiece underside. Therefore a covering layer of elastic material is provided on the upper side of the base. After relaxing the working pressure again, this material returns to its original form each time and is therefore suitable for withstanding very many such elastic compression cycles under high pressure as well as high temperature. By virtue of providing this covering layer, it is now also possible to position the workpiece from below in an appropriate height when operating with vacuum drawing, in order to achieve film coating in the corner regions too without wrinkles. Film coating thereby takes place while the vacuum is building-up. The covering layer reaches its minimum height, in which state its compression is maximum, at the same time as the vacuum reaches its lowest pressure. When pressure is applied thereafter to continue the process, the distance between the workpiece and the supporting plate has become so small that even high pressure will no longer lead to bursting or tearing of the film.
Conventional devices always have to work with a minimum value in relation to the known film properties and thus operate with much greater danger of producing rejects either as film injury or improper film coating.
The covering layer is provided with a gripping surface to prevent slipping of the workpiece.
In a good design the shaft widens from the covering layer to the base and advantageously takes the form of a pyramidal or conical frustrum. This design ensures unproblematic separation of the film from the individual carriers after the pressing process.
According to a further design variant the shaft can also be made in two parts comprising a bottom part connecting to the base for guiding in the range of movement and a top part for taking up the covering layer. The top and bottom part are mutually offset and have no common vertical axis. The eccentric form makes it possible to support workpieces of any shape and dimensions, and the range of movement of the individual carriers becomes even greater.
It is of advantage for the base and the bottom part, as well as top part and the covering lays, to each have a common vertical axis, whereby the upper part carrying the covering layer at least partially projects horizontally beyond the bottom part in the transition region of the two parts. The larger design of the upper part makes possible better loading of the individual carriers.
According to a feature of this invention, the upper part of the shaft is tapered upwards and preferentially has the form of a pyramidal or conical frustrum. This makes it easier to separate the film from the individual carriers after film coating.
The bottom part of the shaft is preferentially cylindrical and chiefly corresponds to the height of the template whose height it exceeds only slightly.
According to a further feature of this invention the guiding plate is equipped with numerous guides which take up the bases of the individual carriers. These guides define the ranges of movement of the individual carriers.
By making the contact bearing area of the base greater than that of the individual carriers, according to a further design variant, unproblematic guiding is ensured without accidental break-out of an individual carrier.
According to a preferred design, the contact bearing area of the base is made rectangular, but variants with rounded corners or completely round designs can be used too.
Rounded elements are of significance in particular for the case in which the base can also be turned in the guide, to prevent binding of the individual carrier in the guides and thus to avoid temporary immobilization. Furthermore, a non-rounded base could come into an inclined orientation in which it could possibly no longer be able to reach the limits of the range of movement. This would imply a restriction of its adjustment possibilities. The rounded forms avoid such difficulties.
It is furthermore envisaged that a template with breakouts is placed above the guiding plate to define the ranges of movement of the individual carriers. At the same time this template also serves to avoid unintentional separation of the individual carriers out of their guides during adjustment, although variants are also conceivable in which one side of the base can already be within the range of movement in the state of maximum displacement. In such cases particular attention must be given to the material of the template so that it does nor become deformed or break under load, because it is not supported by the base. In general the template as well as the guiding plate and the spring plate are made of a porous pressed fibre material. According to a variant, these parts can preferentially be made or aluminum, stainless steel or plastic, if the required strength makes this necessary. In this variant numerous holes are provided for communicating the vacuum. Progressive coating of the workpieces would be hindered without these air passage holes. Porous materials do not require these holes, because of course they are sufficiently permeable for air to communicate the vacuum.
The guiding plate can also be made of wood.
A further design variant of this invention envisages that the base of the individual carrier is spring-mounted in the guide. According to a preferred design of this invention, this is achieved by providing a combination of a spring and a spring plate located in the guide, for taking up the base, whereby the spring is positioned centrally.
In this second variant the shaft extends upwards to a greater extent, for constructional reasons, producing the advantage that the workpieces are moved even closer to the heating device of the coating press during the coating process. The parts to be coated are pre-heated by the radiant heat emitted from the heating plate. The film positioned over the workpieces heats up more quickly, so that the processing time is shortened.
This constellation results in greater edge strength as well as greater surface strength, thus enhanced durability of the produced workpieces.
In this second design variant the spring changes its position after applying the vacuum, thus changing the distance between the workpiece and the press table support. Thereby the elastic covering layer of the individual carriers will hardly contribute, but it is still of advantage to prevent damage to the workpiece underside when applying pressure.
In a further design it is envisaged that several springs are located preferentially in the corner regions of the spring plate.
A further advantage of the spring-loaded design of the individual carriers results from the fact that each individual carrier can easily be separated from its guide by tilting. This makes it very easy to replace damaged carriers or to replace the carriers in general. Furthermore, a variant of the press table insert without using a template is envisaged.
For this purpose the guiding plate consists of a magnetizable material. The base of each individual carrier is thereby held magnetically in the guide and can easily be moved within its adjustment range.
According to a further design variant it is envisaged that the guiding plate is made of two layers comprising a top plate and a bottom plate whereby the guides are provided by the top plate. The top plate is firmly attached to the bottom plate, preferably by bonding.
Another feature of the invention is that the template is equipped with guide pins which pass through the top as well as though the bottom plate, whereby the guide pins pass through the upper plate in the region between the breakouts constituting the guides, and breakouts with clear width above the diameter of the guide pins are provided in the top and bottom plate to take up the guides. Each guide pin is equipped with a stop at its bottom end located in the region of the bottom plate, whereby the clear width of the opening in the bottom plate is above the external diameter of the stop.
The invention also envisages that between the underside of the template and the top side of the stop a sleeve surrounding the guiding pin is provided, and the clear width of the opening through the upper plate exceeds the outer diameter of the sleeve.
When tilting out the individual carriers, the template can definitely be raised through a few millimeters. This considerably facilitates the tilt-out procedure.
According to a variant of the invention, the guide pin is a screw firmly attached to the template.
However, the common height defined by the individual carriers is not equally well suitable for all coating materials. For example, when coating form parts, quite commonly materials arc used which require a smaller than customary separation with respect to the floor already at the beginning of the pressing process, because the resulting pressure would otherwise be too high, entailing a danger of tearing the material. Under such boundary conditions, according to this invention, the effective height of the individual carriers is shortened by interposing an intermediate plate above the template. For this purpose it neither necessary to modify nor to replace the individual carriers themselves. The intermediate plate too has breakouts corresponding to those of the template and defining the movement ranges of the individual carriers. This does not restrict the ranges of movement. But such restriction is possible, if desired, depending on the workpieces or film material.
According to a further design variant of this invention, a preferably elastic filler covering is provided over the template. The surface of this covering is flush with the covering layer of each individual carrier. Any thermally stable material can be used for this filler covering. Cellular rubber or Bulpren are particularly suitable.
The purpose of using such an elastic filler covering is the desired application of greater working pressure which can be combined with stronger pre-heating, giving in turn a higher edge temperature of the produced workpieces. An advantage is that such a coated form board can be exposed to these higher temperatures without separation of the film from the form part, giving a higher quality final product.
After the vacuum drawing step the pressing process interposes a time delay before applying pressure as the next step, to avoid bursting of the film resting on the individual carriers. This time delay can be shortened when using the elastic filler covering which also stabilizes the system and prevents slipping of the workpieces.
To permit restriction of movement of the individual carriers in this variant too, the filler covering is provided with breakouts corresponding to the breakouts of the template, to define the range of movement of the individual carriers.
To improve and speed-up adjustment of the projection of the workpieces, a further extension of this invention envisages marker lines on the surface of the filler covering connecting the outer edges of adjacent breakouts in a row.
Another extension of this invention proposes that plug-on parts should be provided for the individual carriers. This is of great importance in particular for film coating extremely narrow parts which do not permit resting of the workpieces even in minimum setting of the individual carriers. An example of this is film coating of frames. This is a possibility for enlarging the contact bearing surface for such workpieces.
Thereby this invention envisages that a plug-on part encompasses the entire individual carrier and that it is flush with the covering layer on its top side. In order not to impair the elastic effect of the springs carrying the individual carriers, it is envisaged that the upper region of the of the plug-on part has an elastic section which is thicker than the elastic covering layer of the individual carrier. Furthermore, the material of the elastic section is more elastic than the elastic covering layer. This ensures that when vacuum is applied, the elastic section is compressed relatively quickly to the level of the elastic covering layer, beyond which state the spring again acts according to its intended purpose in this invention.
According to a further extension of this invention, it is also envisaged that between adjacent breakouts in the template, further breakouts are provided for regulating the film tension stress. In particular this is intended to prevent wrinkles appearing in the film stretched over the workpieces. This problem arises in particular when the occupation of the press table is rather uneven. The shape of these breakouts is not restricted.
To counteract the enormous tensional stress in the corner regions of the press table, a variant of this invention envisages placement of form pieces in these corner regions. In particular, it is of advantage to give these form pieces triangular cross-section. This reduces the edge effect and thus the tensional stress in this region. Too great pressure in these regions can lead to bursting or discoloration of the film, whereby the discoloration can persist to the next nearest workpiece which therefore becomes a reject item.
Ideally each form piece should be provided with a milled cut on its side facing away from the corners of the press table, to create a gentle transition which further reduces the tensional stress forces.
This invention also includes a process for multi-side film coating of form boards in a press table insert placed in the press table, according to one or several of the features described above, whereby the film located above the form plates resting on the press table is first heated in a heating chamber, and then coated onto the workpiece by applying vacuum and pressure.
The process according to this invention is intended to make possible quicker and more efficient working than the known process is capable of.
This invention solves the task by placing the workpieces, which are to be coated, on the individual carriers with mutual separation, whereby the individual carriers located in the peripheral regions of the workpieces are shifted within their range of movement, such that the relevant individual carriers are slightly set back with respect to the edges of the workpiece, and that after running the press table into the pressing chamber, the distance between the workpieces and the press table support is slightly reduced for the vacuum drawing period.
After sufficient space was available for film coating the edges of the form boards during the vacuum drawing period, thereafter by reducing the separation the space is made so small that the film cannot any longer tear-off or burst when applying the pressure.
A further advantage is achieved by interposing a time delay between the completed vacuum drawing stage and the subsequent application of pressure.
This process step too assists stabilization of the film coating process. Film areas which do not rest on workpieces, but instead on the individual carriers, generally tend to tear if pressure is applied too rapidly. The interposed time delay considerably reduces this tendency.
According to a further extension of this invention, it is also envisaged that for large empty areas between mounted workpieces, form pieces are placed in these empty regions to enhance the film tensioning behavior. Usually adhesive is applied to the sides of the workpieces which are to be film coated, before placing the workpieces onto the press table, and the adhesive is first allowed to dry slightly. This step can be omitted if self-adhesive films are used. However, in this case all individual carriers as well as the press table are treated with a separating agent so that the film can be pulled off again after pressing process.